Auxiliary or secondary wheel assemblies are commonly used to provide improved load distribution on trucks or like vehicles used for hauling heavy loads. The wheel assemblies are not needed in many other circumstances such as when the load has been dumped or otherwise unloaded or when hauling light loads or when the tractor portion of a tractor-trailer is driven alone. Because of this, such auxiliary wheel assemblies typically include a lift mechanism which permits the secondary wheels to be raised out of contact with the ground.
Some of the prior art auxiliary wheel assemblies are capable of being steered in order to overcome steering problems encountered on turns with wheel assemblies wherein the auxiliary wheels are fixed, and one example of such an arrangement is disclosed in U.S. Pat. No. 4,373,738 (Lange). The Lange patent discloses an auxiliary wheel assembly including a transverse axle member extending below the vehicle frame, a king pin assembly on each of the outer ends of the axle member, and a tie rod interconnecting the auxiliary wheels so that the wheels steered together. In one embodiment mentioned in the Lanage patent, the auxiliary wheels are connected to the front wheels of the vehicle through a hydraulic actuation system so that the auxiliary wheels are steered along with the front wheels.
A serious disadvantage of a steering system such as disclosed in the Lange patent wherein the front wheels and auxiliary wheels steer together is the lack of stability provided on turns at high speeds and or with top heavy loads. This lack of stability can result in skidding and slipping and obviously can be very dangerous particularly with larger, heavier vehicles.
Other patents of interest in this field include U.S. Pat. Nos. 4,398,738 (McDaniel); 4,383,696 (Picard); 3,831,210 (Ow); 3,704,896 (Buelow) and 3,390,895 (Verdi), which disclose various forms of retractable wheels assemblies some of which are steerable or capable of being steered.